Single point lasers are used in measurement systems in sawmills to measure various dimensions of a board after it has been through the sawing process. Information from the measurement system can then be analyzed to better control the sawing process for subsequent boards. Measurement of the width of a board, for instance, requires two scanners, positioned on opposite sides of the width dimension of the board. The lasers must be a known, fixed distance apart, with the individual lasers providing distance information from the laser to the edge of the board. With this information, the width dimension of the board can be calculated by the measurement system, as is well known in the art.
Accurate calculation, however, requires regular calibration of the system, which takes into account possible changes in the position of the lasers. A slight change in position can occur in various ways, including temperature change or by the laser support bracket being hit, as examples. Calibration can be carried out manually or automatically. Both methods involve temporarily stopping the sawing process and using a calibration bar. The manual system requires significant involvement by the operator relative to the computer calculations. The automatic system is programmed to look for an object close to the calibration bar size. When the calibration bar is recognized by the automatic system, the system is re-calibrated from the data provided by the lasers to provide a calculated dimension result which is equal to the actual dimension of the calibration bar being scanned. A difficulty with the automatic calculation, however, using a calibration bar, is that the calibration bar must be quite different in the dimensions being scanned than an actual sawn board. If the system is accidentally calibrated using a sawn board, the entire measurement system will be adversely affected. This is, of course, undesirable.
Hence, it is desirable to have an automatic calibration arrangement for board scanning systems in sawmills or similar applications where calibration is reliably and quickly carried out on a calibration bar, with a minimum amount of operator involvement.